Sorting Mined Material

ABSTRACT

A method of sorting mined material for subsequent processing to recover valuable material, such as valuable metals, from the mined material is disclosed. The method includes a combination of selective breakage of mined material (for example, by using microwaves and/or high pressure grinding rolls), subsequent size separation, and then particle sorting of a coarse fraction of the separated material based on differential heating and thermal imaging.

The present invention relates to a method and an apparatus for sortingmined material for subsequent processing to recover valuable material,such as valuable metals, from the mined material.

The present invention also relates to a method and an apparatus forrecovering valuable material, such as valuable metals, from minedmaterial.

The mined material may be any mined material that contains valuablematerial, such as valuable metals.

Typically, the mined material includes mined ores that include mineralsthat contain valuable metals, such as copper and nickel, in sulphideand/or oxide forms.

The present invention is based on a realisation that the use of acombination of selective breakage of mined material (for example, byusing microwaves and/or high pressure grinding rolls), subsequent sizeseparation, and then particle sorting of a coarse fraction of theseparated material based on differential heating and thermal imaging isan effective combination of steps for separating particles that containvaluable material from relatively barren particles with respect to thevaluable material.

The present invention is concerned particularly with rejecting low grademined material, which tends to be in coarse material rather than fines,before it enters a more expensive downstream processing step or steps,such as fine grinding, flotation, leaching, or smelting steps. Rejectinglow grade mined material reduces the amount of mined material to betreated and consequently the cost of the further processing in existingplants. Consequently, rejecting low grade mined material opens upopportunities to reduce processing costs per unit valuable materialrecovered and to free up capacity for more mined material to beprocessed in plants. In some instances the present invention may also beused to make a product for direct sale rather than for furtherprocessing, which is a considerable advantage.

Ore sorting is currently being used for mined material. However, currentsorting methods suffer from difficulties in detecting valuable materialin mined material. Combining ore sorting with selective breakage ofmined material is advantageous because it allows low grade or barrenmaterial in mined material to be identified and at least some of the lowgrade or barren material to be separated using simple sorting apparatussuch as screens or the like. Consequently, more complex sortingapparatus, such as apparatus using air to remove individual particles,is only required to treat a smaller fraction of the mined material.

According to the present invention there is provided a method of sortingmined material, such as mined ore, for subsequent processing to recovervaluable material, such as valuable metals, from the mined material thatincludes the steps of:

(a) breaking particles of mined material and separating the particlesinto at least a coarse fraction and a fines fraction on the basis ofparticle size;

(b) subjecting the coarse fraction of the particles from step (a) tosome form of heating and subsequent thermal imaging analysis andidentifying particles that contain valuable material; and

(c) separating the coarse fraction into (i) particles that containvaluable material on the basis of thermal imaging analysis and (ii)particles that are relatively barren with respect to the valuablematerial.

The amount of the coarse fraction that is processed in step (b) and theamounts of that coarse fraction that are separated for furtherdownstream recovery of valuable material and for disposal as waste willdepend in any situation on the type of mined ore and the valuablematerial of interest and the available downstream recovery processingoptions and the costs of those options. Typically, the amount ofmaterial that is identified as a waste by-product that is not processedin downstream recovery processing options is at least 10%, morepreferably at least 20%, of the mined material. Removing this amount ofmaterial from downstream processing is a significant advantage.

Typically, the fines fraction of the particles from step (a) isprocessed further to recover valuable material from the fines.

The terms “coarse” and “fine” are used herein as relative terms thatdescribe that one fraction has larger particle sizes than anotherfraction. The actual particle sizes that are regarded as “coarse” and“fine” are dependent on the context, i.e. the type of mined material,against which the terms are used.

Typically, the valuable particles from step (c) are processed further torecover valuable material from the particles.

Typically, the remaining particles from step (c) are a waste by-product.

The method may include a step of further breaking the valuable particlesfrom step (c).

Typically, a fines fraction from the further breaking step described inthe preceding paragraph is processed further to recover valuablematerial from the fines. Typically, a coarse fraction from the furtherbreaking step in the preceding paragraph is a waste by-product.

The method may include the steps of subjecting the fines fraction of theparticles from step (a) to thermal imaging analysis and identifyingparticles that contain valuable material and separating the finesfraction into (i) particles that contain valuable material on the basisof thermal imaging analysis and (ii) particles that are relativelybarren with respect to the valuable material.

Typically the valuable particles are processed further to recovervaluable material from the particles.

Typically, the remaining particles are a waste by-product.

The further processing of the valuable particles may be any suitablestep or steps including, by way of example only, heap leaching, pressureoxidation leaching, and smelting steps.

Preferably the basis of thermal imaging analysis is that particles thatcontain higher levels of valuable material will respond differently toat least one heating method than the more barren particles to an extentthat the difference can be detected for example using one of thecommonly available thermal imaging systems based on infrared detectors.These thermal imaging systems are commonly used in areas such asmonitoring body temperature for possible SARS, examining electricalconnections such as in substations, and monitoring tanks and pipes andnow have sufficient accuracy to detect small (i.e. <2° C.) temperaturedifferences.

Preferably step (b) includes heating particles in the coarse fraction byexposing the particles to microwaves, particularly in situations wherethe valuable material and other material in mined materials havedifferent susceptibilities to the microwave energy and therefore heatdifferentially. Most commonly the valuable materials will be much moresusceptible than the other material present and therefore the particleswith higher levels of these valuable materials will become hotter thanthe more barren particles. In any given situation, the selection of thewavelength or other characteristics of the microwave energy will be onthe basis of facilitating a different thermal response of the valuablematerials from the other materials. Different water contents, andtherefore different extents of heating, of the valuable materials andthe other mined materials is one other possible basis for selecting themicrowave energy characteristics. Also, the amounts and/or thedistribution of microwave susceptible minerals, such as sulphides, inthe mined materials are another possible basis for this selection.

Step (a) may be any suitable option or combination of options forbreaking mined material into the coarse fraction and the fines fraction.

One example of a suitable option for step (a) is to use high pressuregrinding rolls.

Preferably step (a) includes using microwave energy to break particlesin the mined material into the coarse fraction and the fines fraction.

The term “microwave energy” is understood herein to mean electromagneticradiation that has frequencies in the range of 0.3-300 GHz.

Preferably step (a) includes using pulsed microwave energy to breakparticles in the mined material.

More preferably step (a) includes using pulsed high energy microwaveenergy to break particles in the mined material.

The term “high energy” is understood herein to mean values substantiallyabove those within conventional household microwaves, i.e. substantiallyabove 1 kW.

Preferably the energy of the microwave energy is at least 20 kW.

More preferably the energy of the microwave energy is at least 50 kW.

More preferably step (a) includes using pulsed high energy microwaveenergy to break particles in the mined material and to heat particles inat least the coarse fraction to a suitable temperature for thermal imageanalysis in step (b).

The use of microwave energy in step (a) may be as described inInternational publication numbers WO 03/102250 and WO 06/034553 in thename of the applicant and the disclosure in the Internationalpublications is incorporated herein by cross-reference.

The use of pulsed microwave energy minimises the power requirements ofthe method and maximises thermal cycling of the ore particles.

Preferably the pulsed microwave energy includes pulses of shortduration.

The term “short duration” is understood herein to mean that the timeperiod of each pulse is less than 1 second.

Preferably the pulse time period is less than 0.1 second.

The pulse time period may be less than 0.01 second.

More preferably the pulse time period is less than 0.001 second.

The time period between pulses of microwave energy may be set asrequired depending on a number of factors.

Preferably the time period between pulses is 10-20 times the pulse timeperiod.

The particles may be exposed to one or more pulses of microwaves toachieve the desired level of micro-cracking for step (a) and heating forstep (b). This can be achieved in a single installation which releasesmicrowave energy in pulses. This can also be achieved in an installationhaving multiple exposure points at spaced intervals along a path ofmovement of the mined material, with each of the exposure pointsreleasing its own characteristic microwave energy in pulses orcontinuously. In some situations the particles may be exposed tomicrowave energy having characteristics selected for heating theparticles and separately exposed to microwave energy havingcharacteristics selected for breaking up the particles. For example,microwave energy for heating particles may be of lower energy and beeither pulsed or continuous unlike that used to achieve fragmentation ofthe particles.

The wavelength of the microwave energy and the exposure time may beselected depending on relevant factors.

Relevant factors may include ore type, particle size, particle sizedistribution, and requirements for subsequent processing of the ore.

The method includes any suitable steps for exposing mined ore tomicrowave energy.

One suitable option includes allowing mined ore to free-fall down atransfer chute past a microwave energy generator, such as described inInternational publication number WO 03/102250.

The free-fall option is one preferred option in a mining industryenvironment because of the materials handling issues that are oftenassociated with the mining industry.

Because the level of heating is small, another option is to pass the orethrough a microwave cavity on a moving bed, preferably a mixed movingbed, with a microwave generator positioned to expose ore to microwaveenergy such as described in International publication number WO06/034553.

The term “moving mixed bed” is understood to mean a bed that mixes oreparticles as the particles move through a microwave exposure zone orzones and thereby changes positions of particles with respect to otherparticles and to the incident microwave energy as the particles movethrough the zone or zones.

Preferably the method includes a step of crushing mined material into amanageable particle size distribution prior to step (a).

Typically, the manageable particle size distribution is one withparticles having a major dimension of less than 100 mm.

Preferably the mined material is in the form of ores in which thevaluable material in the form of metal that is present as a sulphide.

The applicant is interested particularly in copper-containing ores inwhich the copper is present as a sulphide.

The applicant is also interested in nickel-containing ores in which thenickel is present as a sulphide.

The applicant is also interested in uranium-containing ores.

The applicant is also interested in ores containing iron minerals wheresome of the iron minerals have disproportionately higher levels ofunwanted impurities.

The applicant is also interested in diamond ores where the ore has a mixof diamond containing minerals and diamond barren minerals such asquartz.

Preferably the particles of the mined material have a major dimension of15 cm or less prior to exposure to microwave energy in step (a).

According to the present invention there is provided a method forrecovering valuable material, such as valuable metals, from minedmaterial, such as mined ore, that includes sorting mined materialaccording to the method described above and thereafter processing thefines fraction from step (a) and/or other particles containing valuablematerial and recovering valuable material.

The present invention is described further by way of example withreference to the accompanying drawings, of which:

FIG. 1 is a flowsheet of one embodiment of the sorting method inaccordance with the present invention;

FIG. 2 is a flowsheet of another embodiment of the sorting method inaccordance with the present invention; and

FIG. 3 is a flow sheet of another, although not the only other possible,embodiment of the sorting method in accordance with the presentinvention.

The flow sheet of FIG. 1 is described in the context of a method ofrecovering a valuable component in the form of copper fromcopper-containing ores. It is noted that the present invention is notconfined to these ores and to copper as the valuable material to berecovered.

With reference to the flow sheet of FIG. 1, feed material in the form ofore particles that have been crushed by a primary crusher to a particlesize of 10-15 cm, typically less than 10 cm is subjected to selectivebreakage by being treated with pulsed high energy microwave energy.

Specifically, the crushed ore is supplied via a conveyor (not shown—orother suitable transfer means) to a microwave energy treatment station(not shown) and is allowed to free fall past a microwave energygenerator (not shown) that exposes the ore particles to high energypulses of microwave energy.

In an alternative embodiment, although not the only possible otherembodiment, the crushed ore is supplied to an apparatus (not shown) formoving a moving mixed bed of the crushed ore past an exposure zone formicrowaves produced in a microwave energy generator (not shown). Forexample, the moving mixed bed apparatus may be in the form of a screwfeed apparatus.

The microwave energy causes localised heating of the susceptorcomponents of the ore, which typically includes copper-containingminerals, in the ore and the differences in thermal expansion of theconstituents of the ore produces regions of high stress/strain withinthe ore particles and causes micro-cracks to form in the particles,particularly particles containing susceptor components. Invariably, themicro-cracks lead to break down of the particles to smaller particles.

Significantly, the smaller particles tend to contain a higher percentageof copper-containing minerals.

The operating conditions, such as energy level, pulse duration, andexposure length are selected to ensure that the localised heating issufficient to give controlled breakage of the ore particles withoutsignificantly altering the overall composition. The amount of breakagewill depend largely upon how the material is to be further processed buttypically, with an input feed of 10-15 cm particles, the majority of theoutput will have a particle size from 1-15 cm, with a substantialproportion of the output being larger than 5 cm.

The resultant stream of microwave-treated particles is separated inaccordance with particle size into a coarse fraction and a finesfraction.

The fines fraction, which tends to contain more chalcopyrite orchalcocite than the coarse fraction for the reason discussed above, issupplied to a concentrator and thereafter processed to recover copperfrom the particles or to another suitable processing option forrecovering copper.

The coarse fraction is subjected to thermal image analysis to identifyparticles that contain copper-containing minerals.

The basis of thermal imaging analysis insofar as the present inventionis concerned is that particles that contain higher levels of valuablematerial will become hotter than more barren particles.

Advantageously, upstream processing conditions are selected so that theparticles have sufficient retained heat for thermal image analysiswithout additional heating of the particles being required. Ifadditional heating is required, it can be provided by any suitablemeans.

Once identified by thermal image analysis, the hotter particles areseparated from the colder particles and are supplied to the concentratormentioned above and are thereafter processed to recover copper from theparticles.

The colder particles become a by-product waste and are disposed of in asuitable manner.

In general terms, the main aspects of the above-described sorting methodof FIG. 1 are:

(a) microwaves break the feed material selectively, with the rockshaving susceptible minerals being most prone to break due to thedifferential heating—for copper sulphide ores (and nickel sulphide oresand diamond ores)—and such rocks having susceptible minerals usuallybeing a higher grade material and therefore a more valuable component;

(b) size sorting the broken material into a coarse fraction and a finesfraction provides an opportunity to reject some material in the coarsefraction, with the finer fraction generally being richer in the valuablecomponent and being transferred for further processing to the valuablecomponent;

(c) the more valuable particles in the coarse fraction after microwaveexposure can be physically sorted further—the grades can be “measured”using thermal imaging—with the particles having higher levels of thevaluable component such as copper getting hotter than the barrenparticles (with respect to the valuable material) and providing anopportunity to separate the coarse fraction into a more valuablefraction and a less valuable fraction; and

(d) the method being particularly suited for ores which have aheterogeneous distribution of valuable material such as vein-typesulphides commonly found in copper porphyry and nickel sulphides.

The flow sheet of FIG. 2 is an extension of the FIG. 1 flow sheet.

Specifically, the fines fraction from the microwave treatment step issubjected to thermal image analysis in the same way as the coarsefraction.

Once identified by thermal image analysis, the hotter particles areseparated from the colder particles and are supplied to the concentratormentioned above and are thereafter processed to recover copper from theparticles.

The flow sheet of FIG. 3 is an extension of the FIG. 2 flow sheet.

Specifically, the hotter particles from the coarse fraction aresubjected to a further microwave treatment step and the treatedparticles are thereafter separated into a fines fraction and a coarsefraction.

The fines fraction is supplied to the concentrator mentioned above andthe particles in this fraction are thereafter processed to recovercopper from the particles.

The coarse fraction becomes a by-product waste and is disposed of in asuitable manner.

Many modifications may be made to the embodiments of the presentinvention described above without departing from the spirit and scope ofthe present invention.

By way of example, the present invention is not confined to the use ofmicrowaves to selectively break mined material. High pressure grindingrolls are another option.

Moreover, the present invention extends to arrangements in which, forexample, high pressure grinding rolls are used as the means for breakingmined material initially and microwaves are used to further break thecoarse fraction formed in this initial step.

By way of specific example, in an alternative flow sheet (not shown) thebreakage is carried out using mechanical crushing, such as with highpressure grinding rolls, and then the particles are subjected tomicrowave exposure primarily to give differential heating such thathigher copper-containing particles (for example) can be distinguishedfrom the more barren particles and this difference is used to enableseparation.

In this alternative flow sheet the microwave application can be quiteseparate from the crushing and may use lower energy and/or continuousapplication rather than the high energy pulses needed to break theparticles.

The preferred method for heating the ore to enable thermal imaging is touse microwaves to take advantage of their ability to selectively heatcertain components. However, the present invention is not limited to theuse of microwaves and other means may be used to give temperaturedifferences between the mineral components.

The most preferable of these other means is to use the differentresponse of minerals to heat through different thermal conductivitywhereby selected particles within a mix heat up and cool down atdifferent rates to others enabling them to be distinguished andseparated, and through particles with higher water contents not heatingas much as others due to the volatilisation of the water absorbing heatand keeping the particle temperature lower than those particles which donot lose water.

Where these properties are being utilised, conventional heating systemssuch as exposure to hot gas, radiant heating from a heat source and/ordirect contact with a hot surface can all potentially be used.

1-18. (canceled)
 19. A method of sorting mined material for subsequentprocessing to recover valuable material from the mined material,comprising: (a) breaking particles of mined material and separating theparticles into at least a coarse fraction and a fines fraction on thebasis of particle size; (b) subjecting the coarse fraction of theparticles from step (a) to heating and subsequent thermal imaginganalysis and identifying particles that contain valuable material; and(c) separating the coarse fraction into (i) particles that containvaluable material on the basis of thermal imaging analysis, and (ii)particles that are relatively barren with respect to the valuablematerial.
 20. The method of claim 19, further comprising processing theparticles that contain valuable material from step (c) to recovervaluable material from the particles.
 21. The method of claim 19,further comprising processing the fines fraction of the particles fromstep (a) to recover valuable material from the fines.
 22. The method ofclaim 19, further comprising further breaking the valuable particlesfrom step (c).
 23. The method of claim 19, further comprising subjectingthe fines fraction of the particles from step (a) to thermal imaginganalysis and identifying particles that contain valuable material, andseparating the fines fraction into (i) particles that contain valuablematerial on the basis of thermal imaging analysis and (ii) particlesthat are relatively barren with respect to the valuable material. 24.The method of claim 23, further comprising processing the particles thatcontain valuable material further to recover valuable material from theparticles.
 25. The method of claim 19, wherein step (b) includesexposing particles in the coarse fraction to microwaves in order to heatthe particles.
 26. The method of claim 19, wherein step (a) includesusing microwave energy to break particles in the mined material into thecoarse fraction and the fines fraction.
 27. The method of claim 26,wherein step (a) includes using pulsed microwave energy to breakparticles in the mined material.
 28. The method of claim 26, whereinstep (a) includes using pulsed high energy microwave energy to breakparticles in the mined material.
 29. The method of claim 27, wherein theenergy of the microwave energy is at least 20 kW.
 30. The method ofclaim 27, wherein step (a) includes using pulsed high energy microwaveenergy to break particles in the mined material and to heat particles inat least the coarse fraction to a suitable temperature for thermal imageanalysis in step (b).
 31. The method of claim 27, wherein the pulsedmicrowave energy includes pulses of less than 0.1 second.
 32. The methodof claim 31, wherein the pulse time period is less than 0.01 second. 33.The method of claim 27, wherein the time period between pulses is about10 to about 20 times the pulse time period.
 34. The method of claim 19,further comprising crushing mined material into a particle sizedistribution of particles having a major dimension of less than 100 mmparticle size distribution prior to step (a).
 35. The method of claim19, wherein the mined material is in the form of ores in which thevaluable material in the form of metal that is present as a sulphide.36. A method for recovering valuable material, from mined material,comprising sorting mined material according to the method of claim 19,and thereafter, processing the fines fraction from step (a) and/or otherparticles containing valuable material and recovering valuable material.37. The method of claim 25, wherein the valuable material and othermaterial in mined materials have different susceptibilities to themicrowave energy and therefore heat differentially.
 38. The method ofclaim 19, wherein the mined material comprises ore, and the valuablematerial comprises at least one valuable metal.